Snap two objects face to face in object mode?
To do this:


Select the object you want to snap it to the other object
switch to edit mode
switch to face selection
Select the face you want it to be the one touching the other object
Hit Shift+S
choose Cursor to selected
Hit Ctrl + Alt + Shift + C and choose Origin to 3D Cursor
switch to object mode
Select the object you want to snap another object to it
Enter to edit mode
Switch to Face Selection
Select the face you want to snap the other object to
Hit Shift+S
choose Cursor to selected
switch to object mode
Select the object you want to snap it to the other object
Hit Shift+S and choose selected to cursor
That's it
you need to set the origin of the snapped object back to normal using Ctrl + Alt + Shift + C and choose Origin to Geometry